The ASSIST package, which consists of a brief questionnaire, a guide for health professionals on how to use the questionnaire in detecting and responding to substance use and also a self-help manual for cutting down or stopping substance use, is the result of more than 10-years work by WHO and an international group of researchers in the framework of the WHO ASSIST project. It is WHO’s response to the growing demand for guidance on how to best manage problems of substance use in non specialist health care settings. This approach, quick and easy to learn, useful for all substances including alcohol and tobacco, but also cannabis, amphetamine-type stimulants, cocaine and opioids, and with its effectiveness demonstrated in different cultural settings, is set to become a keystone in the health care response to substance use.